guest ::
| Home > Publications database > Ozon-Stickoxid-Korrelationen in der Troposphäre |
| Home > Publications database > Ozon-Stickoxid-Korrelationen in der Troposphäre |
| Book/Report | FZJ-2019-00250 |
; ; ;
1994
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/21175
Report No.: Juel-3008
Abstract: During 13 flights aboard the UK Met. Office Research Aircraft Hercules (C130) around the British Isles in the summers of 1990 and 1991 trace gases in the altitude range 0-10 km were measured in a coilabaration between the ICG-2 of KFA-Jülich and the MRF-Atmospheric Chemistry Group of the UK Met. Office. The measurements include O$^{3}$, NO$_{y}$, NO, H$_{2}$O and hydrocarbons (< C6). In addition, JNO$_{2}$ was determined by a novel photoelectric detectordescribed here. This allowed an estimate of NO$_{x}$ from the simultaneous measurements of NO and O$_{3}$ using the photostationary state assumption. The prevailing meteorological conditions resulted in the southward transport of polar air masses to midlatitudes. In these air masses maximum O$_{3}$ and NO$_{y}$ mixing ratios of 345 ppb and 2600 ppt, respectively, were measured 2 km above the meteorologically defined tropopause (typically 8 km). During different flights the stratospheric NO$_{y}$/O$_{3}$ ratio was found to be constant at (7.6±1)$\cdot$10$^{-3}$ (fig.7.2 p. 96). This ratio also was found as the slope of a linearcorrelation between NO$_{y}$ and O$_{3}$ observed over the whole range of O$_{3}$ mixing ratios between 40 and 345 ppb (fig.7.1 p.94). As it is shown this result has to be explained by mixing between tropospheric air, relatively poor in ozone and NO$_{y}$, and stratospheric air, containing a constant NO$_{y}$/O$_{3}$-ratio. Thus a significant stratospheric contribution to NO$_{y}$ and ozone in the free troposphere can be identified, although the stratospheric source of NO$_{y}$ is relatively small. The correlation between O$_{3}$ and NO$_{y}$ for O$_{3}$ < 100 ppb is similar to that found from otherexperiments as GTE-CITE-2, MLOPEX and AASB (fig. 7.4 p.105). Conversely, measured NO$_{y}$/O$_{3}$ ratios of (3-4.5) $\cdot$ 10$^{-3}$ in the lower stratosphere of midlatitudes (Murphy et al., 1993) are significantly lower than our observed value of (7.6$\pm$1). 10$^{-3}$ in polar air masses. This resultis unlikely to be due to the influence of tropospheric air since we observed slightly smaller NO$_{y}$/O$_{3}$-ratios below the tropopause than above. There are two possible explanations: (1) Photochemical ozone reduction, (2) inhanced influence of aircraft emissions. However, the negative NO$_{y}$-correlation with long lived tracers, such as CF$_{2}$CL$_{2}$ (F12) indicates the absence of extra sources of NO$_{y}$. Model calculations initialized with the NO$_{x}$-data yielded an average ozone production of 5.6 $\cdot$ 10$^{10}$ cm$^{-2}$s$^{-1}$ between 3 and 10 km. In order to quantify the influence of NO$_{x}$ for each model run a second model run was made with identical initialization except for NO$_{x}$ which was set to zero. The difference between the resulting netto ozone production of both runs provides a quantification of the photochemical NO$_{x}$ contribution. The average NO$_{x}$ contribution between 3 and 10 km was 24.4 $\cdot$ 10$^{10}$ cm$^{-2}$s$^{-1}$ neglecting possible effects from non- urethan-hydrocarbons. Measurements in the PBL showed a nonlinear correlation between O$_{3}$ and NO$_{y}$ in photochemically aged airmasses (fig.9.1 p.141) which was due to photochemical ozone production. The observed curvature indicates a nonlinearity of the ozone-ozone precursorrelationship which is in line with results from current photochemical models. As a consequence of the nonlinearity a general reduction of precursor emissions changing neither the spatial and temporal distribution nor the relative contributions from different precursor species probably would cause only a minor change of peak ozone concentrations during smog episodes.
|
The record appears in these collections: |
PDF
PDF (PDFA)